High power fuse

ABSTRACT

A high power fuse consisting of a helically wound fusible element forming an interior space within with heat withdrawing means can be operated.

United States Patent Franklin July 18, 1972 [54] HIGH POWER FUSE 3,116,389 12/1963 Withers ..337/164 x [72] Inventor: LeRoy Franklin, 1016 Castlegate Lane,

2,326,257 8/1943 Schmidt et al ...337/166 [22] Filed: Sept. 17, 1969 2,665,348 1/1954 Kozacka ...337/251 3,453,579 7/1969 Cinquin ..337/161 [21] App]. No.: 858,741

FOREIGN PATENTS OR APPLICATIONS [52] U.S. Cl ..337/185, 337/295 28,872 12/1911 I Great Britain ..337/283 [51] Int. Cl. ..H01h 85/02 1,323,698 3/1963 France ..337/251 [58] Field oiSearch .;...337/185, 166, 222, 57, 228, 23,514 10/1912 Great Britain ..337/222 Primary Examiner-Harold Broome [56] References Cited Attorney-Paul B. Fihe UNITED STATES PATENTS 57] ABSTRACT 1,841,686 1/ 1932 Stephenson.... ..337/253 X A high power f consisting f a helically wound f ibl 1,919,743 7/1933 Pete's "219/364 UX ment forming an interior space within with heat withdrawing 2,758,175 8/1956 l-lotchkiss .....337/104 X means can be operated 2,871,314 l/1959 Swain et al.. ..337/295 X 3,011,038 11/1961 Smith ..337/229 6 Clalns, 3 Drawing figures PATENTEDJULI 81972 3.678.431

CCOLER W I N VEN TOR.

LEROY H. FRANKLIN PATENT AGENT FIELD OF THE INVENTION The present invention generally relates to electrical fuses and more particularly to fuses designed for protection of relatively high power electrical equipment.

BACKGROUND OF THE INVENTION At any power level, it is of course desirable for a fuse to provide fast clearing under short circuit conditions such as a flash-over, capacitor break-down, insulation or cable failure to provide the requisite equipment protection. Such fast clearing time of the blown fuse can be more critical at higher power levels, for example, when the blown fuse must quickly clear or open the circuit to be protected when voltages in a multikilovolt range are experienced. The time for a fuse to clear is obviously determined by the nature of the fusible element, for example, a length of silver wire, and more particularly it is determined by the time required for the fusible element to absorb, enough energy to effect vaporization thereof. Accordingly, it is desirable to minimize the total mass of the fusible element so that this vaporization time is reduced but the consequent minimization of themass of the fusible element such as the mentioned silver wire, in turn, increase its resistance value so that under any given standard operating conditions, an increased voltage drop and consequent heating is the result. If the fuse .is designed to carry a current of, for example, three hundred amperes under normal operating conditions, the heating problem becomes substantial and has, for the most part, required fuse designers to utilize larger diameter fusible elements with a consequent deleterious increase in the clearing time.

The typical fuse is provided with an outer housing to preclude interference from environmental conditions such as high humidity and while some loss of heat through the exterior housing is permitted, under high current conditions, continued operation will generate a substantial amount of heat in the interior spaces of the fuse, thus further agravating the problem.

SUMMARY OF THE INVENTION Accordingly, it is a general objective of the present invention to provide a high power fuse including a highly sensitive fusible element which enables the fuse to clear quickly under overload conditions through the incorporation of means for withdrawing the heat generated by the fuse under normal operating conditions. Generally, such objective is achieved by designing the entire fuse so that heat accumulated within the interior spaces of the fuse is subjected to a heat withdrawing mechanism which effectively transmits the heat to the external environment, thus maintaining the overall fuse temperature at a considerably lower level and accordingly permitting the mentioned use of a smaller mass, increased-sensitivity, fusible element. By way of example, the fuse can be arranged in a tubular configuration so that air or other fluid can be passed through its hollow interior to provide a convective cooling action. Alternatively, a solid member of excellent heat conductive material can be arranged to project into the interior space within the fuse body and to also project outwardly beyond its extremities whereat radiating fins will allow radiation transfer of heat flowing through such heat conductive body to the exterior of the fuse. As yet another alternative, a heat conductive body can be inserted into the interior space of the fuse and, in turn, can be provided with internal passages through which a cooling fluid can be pumped to provide a particularly effective heat withdrawal mechanism. Obviously, various combinations of heat withdrawing mechanisms utilizing radiation, conduction, or convection can be visualized based on the foregoing examples.

BRIEF DESCRIPTION OF THE DRAWING The stated objective of the invention and manner in which it is achieved as summarized hereinabove will be more readily understood by a perusal of the following description of the exemplary embodiments of the invention illustrated in the accompanying drawing wherein:

FIG. 1 is a side elevational view of a high power fuse embodying the invention, a portion of the structure being broken away to illustrate interior details, the fuse structure being illustrated in operative association with a diagrammatically illustrated fan,

FIG. 2 is a side elevational view of a modified form of fuse embodying the invention, again portions being broken away to illustrate interior details of its construction, and

FIG. 3 is a side elevational view of another fuse embodying the invention, with portions broken away to illustrate details of its interior structure, and illustrated in operative association with an external recirculating fluid cooling system which is merely indicated diagrammatically.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION With initial reference to FIG. 1, the illustrated high power fuse 10 is of generally tubular configuration with a central in terior cylindrical space 12 extending entirely therethrough. The fuse is formed by an external hollow cylindrical tubular section 14 of insulating material preferably in the form of epoxy fiberglass tubing having metal annular plates forming the opposite fuse terminals 16, 18 at the ends of the fuse to which the exterior circuitry can be suitably attached. The hollow tubular fuse housing is completed by a smaller diameter section 20 of epoxy tubing supported between the end terminals and their inner peripheries in essentially concentric relation with the outer tubing section 14 through the medium of annular metal rings 21 bolted to the inner surfaces of the annular terminal plates only one ring being shown. Preferably, sealed interconnections of any suitable type are made so that the annular space between the two concentric tubing sections 14, 20 is hennetically sealed.

The fusible element 22 in the illustrated structure takes the form of an elongated piece of silver wire connected at its opposite extremities to the two rings 21 and accordingly to the terminal plates l6, l8 electrically and physically connected thereto and extending in a wound helical path around a plurality of insulating rods 24 preferably of ceramic material physically supported between the mounting rings 21 at circumferentially spaced positions.

Specifically, a fuse of the type illustrated designed to carry three hundred amperes under normal operating conditions and capable of clearing 35 kilovolts DC when blown may include as the fusible element six wires wound in helical parallelism in one direction and another six counter wound in helical parallelism in the opposite direction, the diameter of each silver wire being approximately 0.0187 inches, the overall length of the fuse body in such case being approximately forty inches. With such small wires, the clearing time will approximate no more than a few microseconds.

Obviously, considerable heat will be generated by such fuse with such small silver wires as the fusible elements 22 and operating normally at three hundred amperes and such heat will tend to accumulate within the hollow interior of the tubular fuse 10. If the fuse 10 is supported in a vertical position, the heat will tend to rise and a natural convection flow of air therethrough will remove a portion of the heat and depending upon environmental conditions, such flow may effect heat withdrawal from the fuse sufficient to preclude malfunction. However, as illustrated, it is preferred to employ artificial means for withdrawing heat in the form of a motor driven fan 26 which directs a draft of air through the tubular interior of the fuse body 10 and it is preferred moreover to automatically increase the speed of fan rotation and the created draft of air through the tubular fuse automatically in response to an increased flow of current through the fusible element 22. Quite simply, this may be achieved by inserting a resistor 28 in series with the fuse circuit so as to generate a voltage thereacross which increases with fuse current and the motor which drives the fan 26 is, in turn, a voltage variable speed motor which is connected across such resistor and whose rate of rotation increases as the voltage across the resistor increases.

The structure described hereinabove and illustrated in FIG. I obviously constitutes a heat withdrawing mechanism in the form of convective cooling. Alternate heat withdrawing means is embodied in the alternate embodiment shown in FIG. 2 wherein the fuse structure itself is generally similar to that illustrated in FIG. 1 wherefore like reference numerals will be applied to corresponding parts with but the addition of a prime notation to provide differentiation. Again a tubular section 14' of epoxy fiberglass material is supported between two terminals 16, 18' which, however, take the form of circular plates arranged in hermetically sealed relation with the epoxy tubing to form a sealed housing. Annular rings 21 are supported within each of the terminals 16', 18 to, in turn, support'anumber of ceramic insulating rods 24 which, in turn, support the fusible element or elements 22 of the fuse 10' in a helical configuration. Since the ends of the fuse 10 are enclosed, no interior tubing is necessary. From each terminal plate l6, 18 a conical rod 30 of highly heat conductive material suchas aluminum projects inwardly into the interior fuse space 12, the end of each rod being rounded and spaced from the end of the other rod a sufiicient distance to preclude arcing therebetween when the fuse l blows. Preferably, a threaded stud (not shown) projects from the outer end of each of the conical rods 30 through a central opening in the terminal plate 18' and has attached by a screwed interconnection on the exterior of the terminal plate, a radiator 34 formed by highly conductive metal material such as aluminum in the form of a central rod with a plurality of integral annular radiating fins projecting outwardly therefrom in spaced relationship. Accordingly, heat generated within the fusible element 22 passes into the interior spaces of the fuse l0 and is absorbed in the conical aluminum rod 30 to be conducted through it to the exterior radiation 34 whereat it is exposed to the cooler exterior environmental conditions thus to provide transfer of heat from the fuse interior to the exterior environment.

The first embodiment of the invention illustrated in FIG. 1 utilized the heat withdrawing means which was primarily convective in nature and the second embodiment provided a mechanism utilizing conduction and radiation of heat. A third embodiment of the invention, as illustrated in FIG. 3, is arranged to utilize a combination of conduction and convection in its heat withdrawing process.

The basic fuse structure of FIG. 3 is quite similar to that illustrated and described hereinabove with respect to FIG. 2 and corresponding elements will accordingly be indicated by like numerals with an added double prime notation to enable differentiation. An exterior cylindrical tubular section 14" of epoxy fiberglass is joined at its opposite extremities to terminals 16",18" which in this instance include a relatively thick circular plate which can be integrally cast out of aluminum with an interiorly projecting frusto-conical or approximately hemispherical section that projects into the interior space 12" within the fuse at each end. The circular plate portions of the terminals 16", 18" are sealed to the tubular epoxy section 14" to form a hermetically closed housing within which the fusible elements 22" in the form or silver wires are connected at their extremities to the terminal plates and at intermediate positions are wound helically around circumferentially spaced parallel ceramic rods 24" supported at extremities by the terminal plates much in the fashion of the previous described embodiments of the invention.

Within the thickened end plate and the inwardly projecting conical or hemispherical portion of each terminal l6", 18 is formed an interior passage 36 that extends from the side of the end plate inwardly and thence curves in a path through the interior of the inwardly projecting portion to once again emerge through a radial passage which erminates at the opposite si e of the thickened end plate. The terminal ends of the passage 36 are provided with suitable connectors (not shown) that enable closed juncture therewith of an external fluid coolant supply system including suitable conduits diagrammatically indicated at 38 connected to an exterior pump 40 and cooler 42 so that fluid preferably of insulating substance such as oil or Freon can be continuously recirculated through the interior passage 36 so that heat withdrawn from the fuse 10 under normal operation will pass through the heat conducting aluminum projecting portions of the structure into the moving fluid and thereafter be withdrawn during flow thereof through the exterior cooler 42. Although but one interior passage 36 is shown, it will be obvious that a multiplicity thereof can be connected in parallel to yet further enhance the cooling operation.

Various combinations of the exemplary cooling mechanisms can be envisioned to allow the use of the smaller and thus more sensitive fusible elements wherefore rapid effective clearing of the fuse is assured.

What is claimed is:

1. A high power fuse which comprises a plurality of parallel, circumferentially-spaced insulating rods,

a fusible element wound around said rods to form an interior space, and means including a heat conductor projecting from an exterior position into said interior space for withdrawing heat generated by flow of current through said fusible element from the interior space to a position exterior of the fuse,

said rods constituting the only structure between said fusible element and said heat conductor thereby allowing optimal heat transfer therebetween.

2. A high power fuse according to claim 1 wherein,

said conductor has radiating fins on the projecting exterior portion thereof.

3. A high power fuse according to claim 1 wherein,

said heat conductor includes an interior passage through 4. A high power fuse according to claim 3 which comprises,

means connected to said interior passage for pumping fluid therethrough.

5. A'high power fuse according to claim 4 which comprises,

means for cooling said fluid at a position exterior of said interior space.

6. A high power fuse according to claim 4 wherein,

said pumping means is connected to said interior passage in a closed system whereby fluid is continually recirculated. 

1. A high power fuse which comprises a plurality of parallel, circumferentially-spaced insulating rods, a fusible element wound around said rods to form an interior space, and means including a heat conductor projecting from an exterior position into said interior space for withdrawing heat generated by flow of current through said fusible element from the interior space to a position exterior of the fuse, said rods constituting the only structure between said fusible element and said heat conductor thereby allowing optimal heat transfer therebetween.
 2. A high power fuse according to claim 1 wherein, said conductor has radiating fins on the projecting exterior portion thereof.
 3. A high power fuse according to claim 1 wherein, said heat conductor includes an interior passage through which fluid may flow.
 4. A high power fuse according to claim 3 which comprises, means connected to said interior passage for pumping fluid therethrough.
 5. A high power fuse according to claim 4 which comprises, means for cooling said fluid at a position exterior of said interior space.
 6. A high power fuse according to claim 4 wherein, said pumping means is connected to said interior passage in a closed system whereby fluid is continually recirculated. 